The present invention relates to a rapid-acting flow modulation valve designed to modulate a fluid flow in response to an externally supplied control signal commanding at an extremely high rate. The flow modulation valve incorporates pressure balanced throttling components, a fast-acting coil actuator, low hysteresis movement, and an energy-dense magnetic geometry in order to produce high frequency flow modulation in response to input drive signals. The flow modulation valve may be utilized for applications requiring readily amenable retrofitting, small diameter working fluid lines, high operational frequency, strict controllability, and low production and maintenance cost, among other advantages. An embodiment of the flow modulation valve is designed to operate in high temperature, high line pressure environments where rapid flow modulation is advantageous or required, such as gas turbine active combustion control systems, variable valve timing engines, or other applications requiring high speed throttling operations.
Throttle valves are used in industry in a variety of applications requiring control of fluid flow. The majority of these applications require throttling valve action at a relatively low speed, often in a stepwise manner, and at relatively low temperatures and pressures. A number of suitable valves have been developed for the relatively slow, lower temperature and pressure applications, including globe valves, gate valves, and various rotary-type valves. The operating mechanics of low-frequency, precise throttling operations are well developed and understood.
Development of higher frequency flow modulation applications, however, presents additional challenges. Higher frequencies obviate manual valve actuation, and the hydrodynamic interaction between moving valve parts and the throttled flow demands careful evaluation of the flow structure throughout the valve. Simplicity of operation also plays a much more significant role, as the higher frequencies desired demand that valves provide throttling actions over a much shorter response time. As a result, the requirement for synergy between all components involved in the execution of a throttling action is much greater than with a low frequency valve application, and high frequency flow modulating valves must be developed and optimized as a whole system to a much greater degree.
Some methods of high frequency modulation utilize smaller valves having extremely short open/shut switching times. These two-position valves operate in a digital mode rather than proportional analog valves, and are driven by a pulse-width modulated control signal for quasi-analog operation. Precise flow control can be achieved by configuring multiple digital valves into assemblies, where successive valves in the assembly may have differing flow capacity. Valve operation in this technique is binary in nature with only an open or closed state. See, e.g., Cornwall et al, U.S. Patent Application Publication 2007/0151252, published Jul. 5, 2007. A variation on the digital valve technique utilizes rotating discs that align flow orifices on each disc at a specified frequency. These devices likewise operate by utilizing a digital mode to accomplish quasi-analog high frequency flow modulation. See, e.g., U.S. Pat. No. 7,114,336, issued to Hommema et al., Oct. 3, 2006. These approaches have achieved some success, however the use of digital combinations to approximate a desired analog characteristic generates inherent inaccuracies and typically requires microprocessor control. Additionally, the on/off injection methodology is unable to modulate both the amplitude and the phase of a fuel injection, unlike a proportional injection methodology. Additionally, general size and high pressure and temperature effects on the mechanism may prohibit operations in applications where a small footprint and large variation in thermal stresses become significant. In some applications, it would be advantageous to provide a fast-acting, high frequency flow modulation valve that utilizes proportional control, rather than various digital combinations, to affect flow modulation about a mean rate.
Other methods of high-frequency flow modulation rely on rapid actuation of spool valves. Typically, a source signal is conditioned by a servo controller and then amplified by a power amplifier. The spool moves axially in response to the signal producing a spool displacement. The spool displacement is measured by a transducer, which feeds this signal back to the servo controller. This simple control method produces spool motion which is proportional to an electrical signal input, and the flow magnitude is related to the spool displacement. However, in order to achieve an adequate degree of flow modulation with a short response time, the spools typically control multiple flow passages to increase the flow rate achieved with shorter strokes. This increases the necessary size of the spool. As a result, for high frequency and large flow rate applications, the force and power required of the actuator in order to stroke the spool becomes significant, and single stage spool valves can become impractical in terms of size and valve geometry. Efforts toward high frequency spool valve operation are typically geared toward reduction of the force requirement necessary for rapid spool movement. See for example U.S. Pat. No. 5,460,201 issued to Borcea et al., Oct. 24, 1995, among others. For these reasons, in many applications, a valve where sufficient throttling is achieved through manipulation of a single flow restriction, in order to reduce the necessary mass of the moving component and thereby reduce the response time of the valve for a given value of actuator force provided, may be desired. Further, such an arrangement could avoid the high differential pressures developed from low pressure ports to high pressure ports in spool valves, greatly reducing concerns over maintaining hydraulic balance in the operating environment so that higher frequency capabilities are not degraded.
Successful high frequency flow modulation also clearly requires an actuator sufficient to drive valves to high frequency operation. Magnetic stroke actuators are often utilized, although alternate actuator principles exist. The high frequency operation levies a general requirement that the actuator perform adequately in a direct drive configuration. Direct drive here means that there is no amplification of an electrical command signal required in order to affect valve movement. This avoids the limited bandwidth experienced by many lower frequency valves, which trade-off the increased response time generated by signal amplification in order to take advantage of lower power electrical command signals. In direct drive systems, conversely, a single, directly controlled system develops the force necessary to shuttle the valve. In addition to increasing the response, this approach also simplifies the internal component arrangement. However, generating the energy density and force necessary to achieve a desired bandwidth for a given device size with a direct drive arrangement is a formidable challenge. In some cases, the force required to accelerate the valve mass can be high, and physically large electromagnetic actuators may be required. Additionally, impinging flows on the throttling elements of the valve add additional actuator force requirements, further increasing the size of the actuator. In applications where the overall size of the high frequency flow modulator is a concern, lower mass moving components and an internal flow geometry minimizing impinging flow on the throttling components offer an advantage.
Additionally, a high frequency flow modulating valve designed for compactness of the overall mechanism may generate pressure and temperature concerns, depending on the operating environment. A high frequency valve designed to optimize actuator capabilities, reduce valve mass, and minimize overall valve size may be subject to tight tolerances between components. In high temperature environments, disregard of differing thermal characteristics among valve components may significantly alter these tolerances, producing drastic effects on the operational frequency obtainable from moving components. Similarly, differing expansion characteristics may induce stresses that significantly reduce operational lifetime. These effects can become highly significant if the valve assembly is subject to large thermal cycles. For example, a gas turbine flow modulation valve may be at ambient temperature during shutdown or maintenance, and subsequently experience rapid heat-up and operation at temperatures exceeding 600° F. due to turbine fuel preheat. This concern may be particularly pertinent in flow modulation applications for control of combustion instability. In such applications, the resonant responses and time delays of the fuel system between the modulating valve and the combustion turbine must be carefully evaluated, and reducing or eliminating the downstream fuel system is the best way to achieve control authority. However, this may not be possible for many existing actuators, because the actuators are too sensitive for reliable and consistent operation in the high temperature environment that exists in close proximity to the combustion turbine. As a result, in applications where significant thermal cycling is expected, the thermal characteristics of the valve components, in terms of material utilized, component geometry and the resulting impact on actuator sensitivity, becomes a highly significant factor.
The manner in which fluid pulses are integrated into the fluid flow in order to produce the flow modulation also has significant impact. Often the techniques utilize a pilot flow and a main flow. Flow pulses are generated in the pilot flow using an applicable technique, and the pilot flow and the main flow are then combined. This generates a fluid pulsation occurring generally about the main flow rate. The necessity to combine multiple flowpaths in this arrangement adds to the footprint of the flow modulator, and can preclude use in situations where space constraints apply. Additionally, the required amplitude of modulation required in the pilot flow may be significant, depending on the relative magnitudes of the pilot flow and the main flow. This may dictate longer valve strokes for adequate pilot flow pulsation, and the inertia of moving parts over the stroke can reduce the actuator's responsiveness. In some applications, it would be advantageous to utilize a valve assembly designed to transfer the full mass flow rate of fluid and introduce the pulsation directly, without the need for superposition.
Accordingly, it is an object of the present invention to provide a rapid-acting, compact, high frequency flow modulation valve optimizing the interactions among all components involved in the execution of a throttling action, by utilizing a unique synergy between the valve actuator, moving and fixed valve components, and hydrodynamic interactions between the throttled flow and the valve.
Further, it is an object of the present invention to provide a rapid-acting, compact, high frequency flow modulation valve that utilizes traditional flow restriction characteristics, rather than various digital combinations, to affect flow modulation about a mean rate.
Further, it is an object of the present invention to provide a rapid-acting, compact, high frequency flow modulation valve that reduces the necessary mass of the moving components and thereby reduces the response time of the valve for a given value of actuator force provided.
Further, it is an object of the present invention to provide a rapid-acting, compact, high frequency flow modulation valve that minimizes hydraulic imbalances on moving components in the operating environment, so that higher frequency capabilities are not degraded.
Further, it is an object of the present invention to provide a rapid-acting, compact, high frequency flow modulation valve that provides an internal flow geometry which minimizes impinging flows on the throttling elements of the valve, further reducing the response time of the valve for a given value of actuator force provided.
Further, it is an object of this disclosure to provide a rapid-acting, compact, high frequency flow modulation valve providing a geometry compatible with the thermal characteristics among valve components, so that temperature cycles encountered during normally expected operation do not degrade necessary physical tolerances, induce stresses that significantly reduce operational lifetime, or drive actuator sensitivity below useful levels.
Further, it is an object of the present invention to provide a rapid-acting, compact, high frequency flow modulation valve designed to transfer the full mass flow rate of fluid and introduce flow pulsations directly on the full mass flow rate, without the need for superposition of a pulsed pilot flow.
These and other objects, aspects, and advantages of the present invention will become better understood with reference to the accompanying description and claims.